For purposes of this discussion, an RFID transponder generally comprises a substrate, an RFID chip or chip module (CM) disposed on or in the substrate, and an antenna disposed on or in the substrate. The transponder may form the basis of a secure document such as an electronic passport, smart card or national ID card, which may also be referred to as “data carriers”.
The RFID chip (CM) may operate solely in a contactless mode (such as ISO 14443), or may be a dual interface (DI, DIF) chip module (CM) which may additionally be operative to function in a contact mode (such as ISO 7816-2) and a contactless mode. The RFID chip (CM) may harvest energy from an RF signal supplied by an external RFID reader device with which it communicates.
The substrate, which may be referred to as an “inlay substrate” (such as for electronic passport) or “card body” (such as for smart card) may comprise one or more layers of material such as Polyvinyl Chloride (PVC), Polycarbonate (PC), polyethylene (PE), PET (doped PE), PET-G (derivative of PE), Teslin™, Paper or Cotton/Noil, and the like.
A chip module (CM) may be a leadframe-type chip module or an epoxy-glass type chip module. The epoxy-glass module can be metallized on one side (contact side) or on both sides with through-hole plating to facilitate the interconnection with the antenna.
An antenna, which may be referred to as a “card antenna” (CA), may be mounted to the inlay substrate using a sonotrode (ultrasonic tool) and electrically connected with the chip module (CM). See, for example U.S. Pat. No. 6,698,089 and U.S. Pat. No. 6,233,818, incorporated by reference herein. A typical pattern for a card antenna (CA) is generally rectangular, in the form of a flat (planar) coil (spiral) having a number of turns, disposed around the periphery of the substrate (or relevant portion thereof). See, for example, U.S. Pat. No. 7,980,477.
Rather than directly electrically connecting the RFID chip (CM) to a card antenna (CA), a module antenna (MA) may be incorporated into an antenna module (AM) comprising the RFID chip (CM) and the module antenna (MA). The module antenna (MA) may be quite small (such as approximately 15 mm×15 mm), in contrast with the card antenna (CA) (such as approximately 50 mm×80 mm).
U.S. Pat. No. 5,084,699 (Trovan, 1992) entitled Impedance Matching Coil Assembly For An Inductively Coupled Transponder. Attention is directed to FIG. 5. A coil assembly for use in an inductively powered transponder includes a primary coil (156) and a secondary coil (158) wrapped around the same coil forming ferrite rod (160). The primary coil's leads (162) are left floating while the secondary coil's leads (164) are connected to the integrated identification circuit of the transponder.
U.S. Pat. No. 5,955,723 (Siemens, 1999) entitled Contactless Chip Card discloses a data carrier configuration includes a semiconductor chip. Attention is directed to FIG. 1. A first conductor loop (2) is connected to the semiconductor chip (1) and has at least one winding and a cross-sectional area with approximately the dimensions of the semiconductor chip. At least one second conductor loop (3) has at least one winding, a cross-sectional area with approximately the dimensions of the data carrier configuration and a region forming a third loop (4) with approximately the dimensions of the first conductor loop (2). The third loop (4) inductively couples the first conductor loop (2) and the at least one second conductor loop (3) to one another.
U.S. Pat. No. 6,378,774 (Toppan, 2002) entitled IC Module and Smart Card. Attention is directed to FIGS. 12A,B and 17A,B. A smart card comprises an IC module and an antenna for non-contact transmission. The IC module has both a contact-type function and a non-contact-type function. The IC module and the antenna comprise first and second coupler coils, respectively, which are disposed to be closely coupled to each other, and the IC module and the antenna are coupled in a non-contact state by transformer coupling.                Toppan's antenna (4) comprises two similar windings (4a, 4b), which are shown in FIG. 17A disposed on opposite sides of a substrate (5), one substantially atop the other. A coupler coil (3) is associated with the card antenna (4). Another coupler coil (8) is associated with the chip module (6). As best viewed in FIGS. 12A and 12B, the two coupler coils (3, 8) are of approximately the same size and are disposed substantially one atop the other.        
U.S. Pat. No. 7,928,918 (Gemalto, 2011) entitled Adjusting Resonance Frequency By Adjusting Distributed Inter-Turn Capacity discloses a method for adjusting frequency tuning of a resonant circuit with turns having a regular spacing generating stray inter-turn capacity.
US 2009/0152362 (Assa Abloy, 2009; issued as U.S. Pat. No. 8,130,166) discloses Coupling Device For Transponder And Smart Card With Such Device. Attention is directed to FIG. 6. A coupling device is formed by a continuous conductive path having a central section (12) and two extremity sections (11, 11′), the central section (12) forming at least a small spiral for inductive coupling with the transponder device, the extremities sections (11, 11′) forming each one large spiral for inductive coupling with the reader device.                Assa Abloy '166 shows that the inner end of the outer extremity section (11) and the outer end of the inner extremity section (11′) are connected with the coupler coil (12). The outer end (13) of the outer extremity section (11) and the inner end (13′) of the inner extremity section (11′) are left unconnected (loose).        
US2010/0176205 (SPS, 2010) entitled Chip Card With Dual Communication Interface. Attention is directed to FIG. 4. A card body (22) includes a device (18) for concentrating and/or amplifying electromagnetic waves, which can channel the electromagnetic flow received, in particular, from a contactless chip card reader toward the coils of the antenna (13) of the microelectronic module (11). The device (18) for concentrating and/or amplifying electromagnetic waves may consist of a metal sheet disposed in the card body (22) below the cavity (23) receiving the microelectronic module (11), or may consist of an antenna consisting of at least one coil, disposed in the card body (22) below the cavity (23) receiving the microelectronic module (11).
All of the patents and publications referenced herein are “incorporated by reference”, including the following: CA 2,279,176; DE 4311493; U.S. Pat. No. 6,142,381; U.S. Pat. No. 6,310,778; U.S. Pat. No. 6,406,935; U.S. Pat. No. 6,719,206; US 2009/0057414; US 2010/0283690; and US 2011/0163167.